Light sources, such as fluorescent and mercury lamps, which repeat flashing of light at twice the frequency of a fixed power frequency has been widely used to achieve sufficient brightness inside of the room or the like. Under such a light source, if image capture is performed in a rolling shutter mode in which exposure timing is different for each line, a component having luminance varying at a fixed frequency along the direction perpendicular to the line occurs in image data, which causes a phenomenon that appears as a horizontal stripe. This horizontal stripe is caused by difference between the power frequency of a light source and a horizontal synchronization frequency that scans the line, and thus is called a flicker component. Furthermore, the position of a flicker component in the image data, that is, the phase may vary for each frame (or a field) in a moving image. The amount of variation in phases for each frame when a phase varies is determined from the power frequency of a light source and a vertical synchronization frequency of an image sensor.
In one example, in a case where the power frequency is 50 hertz (Hz) and the vertical synchronization frequency is 59.94 hertz (Hz), the amount of variation in phases for each frame is approximately one third (⅓) of a period of a vertical synchronization signal. Thus, the phase of a flicker component completes one cycle through three frames and returns to a phase that is substantially the same as that prior to the three frames.
An image capturing device capable of determining whether a flicker component is present by calculating an average value for each line of three successive frames in time series is developed (e.g. see Patent Literature 1). This image capturing device determines whether a flick component is present based on a result obtained by dividing each line of a current frame by an average value of the corresponding lines of three successive frames including the current frame. Then, the image capturing device, when determining that a flicker component is present, removes the flicker component from image data, thereby improving the image quality of the image data.